Document JP 11 072132 discloses a suspension comprising a shock absorber having a first portion and a second portion that are slidably movable relative to each other, the shock absorber being fitted with a wave transceiver assembly disposed on the first movable portion, the transmitter being disposed to transmit the wave towards the second movable portion, and the receiver being suitable for receiving the wave after it has been reflected on an obstacle formed by a mechanical part secured to the second movable portion.
By measuring the travel time of the wave, it is possible to deduce the compression of the shock absorber.
In a variant mentioned in that document, the shock absorber is fitted with a transceiver assembly adapted to send a wave to an obstacle formed by the free surface of a hydraulic fluid contained in the shock absorber or a mechanical part defining said free surface.
By measuring the travel time of the wave, it is possible to deduce the real level of hydraulic fluid in the shock absorber. By knowing the relationship between shock absorber compression and the theoretical level of hydraulic fluid in the shock absorber, it is possible to deduce therefrom the extent to which the shock absorber is compressed.
However, applying that method assumes that the shock absorber was properly conditioned and has not suffered any leakage of hydraulic fluid, such that the theoretical level of hydraulic fluid and the real level of hydraulic fluid are the same.
If an incorrect quantity of hydraulic fluid was introduced into the shock absorber, or if the shock absorber has suffered from leakage, then the real level of hydraulic fluid can be different from the theoretical level of hydraulic fluid, so that the wrong degree of compression is deduced therefrom.